[111.05] Eta Carinae: The Central Star

Recent HST STIS observations have revealed the spectrum of
the central star in Eta Carinae for the first time. These
observations clearly show that the optical spectrum of the
central star is dominated by emission lines of H,
\ion{He}{1}, and \ion{Fe}{2}. Its spectrum is qualitatively
similar to the extreme P Cygni star HDE\,316285.

Using the non-LTE atmosphere code of Hillier and Miller
(1998) we have performed a spectroscopic investigation of
the central star. Previously measured IR fluxes indicate
that the luminosity of the system is approximately 5\times
106\,L\odot (for a distance of d=2.5\,kpc), which we
adopt as the luminosity of the central star. An excellent
fit is obtained to the emission line spectrum using a mass
loss rate of 10-3M\odot\,yr-1, a terminal wind
velocity of \approx 500\,kms-1, and a solar Fe
abundance (by mass). Due to degeneracies in the model it is
difficult to constrain both the effective temperature and
the H/He abundance ratio.

The most significant discrepancy is that the strength of the
P Cygni absorption components is overestimated, particularly
on the \ion{Fe}{2}\ emission lines. These discrepancies may
be due to asymmetries in the stellar wind and/or time
variability. There may also be a problem for our models in
matching the UV spectrum shortward of 1600Å, but STIS
observations of the central star are not yet available,
while earlier GHRS observations may be contaminated by
nebula emission and/or a companion star.

We discuss the implications of our results for the current
evolutionary status of \eta\,Car, and for the binary model
of Damineli et\,al. (1997).

This research was supported in part by NASA through a grant
from the STScI, which is operated by AURA, under NASA
contract NAS5-26555. Additional support was provided by NASA
grant NAG5-8211.